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class="sidebar-heading"><span>实战案例</span> <!----></p> <ul class="sidebar-links sidebar-group-items"><li><a href="/md/concurrent/ActualCombat/default.html" class="sidebar-link">关于我</a></li></ul></section></li><li><section class="sidebar-group depth-0"><p class="sidebar-heading"><span>面试</span> <!----></p> <ul class="sidebar-links sidebar-group-items"><li><a href="/md/concurrent/interview/default.html" class="sidebar-link">关于我</a></li></ul></section></li><li><section class="sidebar-group depth-0"><p class="sidebar-heading"><span>系统架构</span> <!----></p> <ul class="sidebar-links sidebar-group-items"><li><a href="/md/concurrent/framework/default.html" class="sidebar-link">关于我</a></li></ul></section></li></ul> </aside> <div><main class="page"> <div class="theme-default-content content__default"><h1 id="【高并发】深入解析callable接口"><a href="#【高并发】深入解析callable接口" class="header-anchor">#</a> 【高并发】深入解析Callable接口</h1> <p><strong>大家好，我是冰河~~</strong></p> <p>本文纯干货，从源码角度深入解析Callable接口，希望大家踏下心来，打开你的IDE，跟着文章看源码，相信你一定收获不小。</p> <h3 id="_1-callable接口介绍"><a href="#_1-callable接口介绍" class="header-anchor">#</a> 1.Callable接口介绍</h3> <p>Callable接口是JDK1.5新增的泛型接口，在JDK1.8中，被声明为函数式接口，如下所示。</p> <div class="language-java line-numbers-mode"><pre class="language-java"><code><span class="token annotation punctuation">@FunctionalInterface</span>
<span class="token keyword">public</span> <span class="token keyword">interface</span> <span class="token class-name">Callable</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">V</span><span class="token punctuation">&gt;</span></span> <span class="token punctuation">{</span>
    <span class="token class-name">V</span> <span class="token function">call</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token keyword">throws</span> <span class="token class-name">Exception</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br></div></div><p>在JDK 1.8中只声明有一个方法的接口为函数式接口，函数式接口可以使用@FunctionalInterface注解修饰，也可以不使用@FunctionalInterface注解修饰。只要一个接口中只包含有一个方法，那么，这个接口就是函数式接口。</p> <p>在JDK中，实现Callable接口的子类如下图所示。</p> <p><img alt="" data-src="https://img-blog.csdnimg.cn/20200217142658360.png" loading="lazy" class="lazy"></p> <p>默认的子类层级关系图看不清，这里，可以通过IDEA右键Callable接口，选择“Layout”来指定Callable接口的实现类图的不同结构，如下所示。</p> <p><img alt="" data-src="https://img-blog.csdnimg.cn/2020021714283326.png" loading="lazy" class="lazy"></p> <p>这里，可以选择“Organic Layout”选项，选择后的Callable接口的子类的结构如下图所示。</p> <p><img alt="" data-src="https://img-blog.csdnimg.cn/20200217142906212.png" loading="lazy" class="lazy"></p> <p>在实现Callable接口的子类中，有几个比较重要的类，如下图所示。</p> <p><img alt="" data-src="https://img-blog.csdnimg.cn/2020021714294241.png" loading="lazy" class="lazy"></p> <p>分别是：Executors类中的静态内部类：PrivilegedCallable、PrivilegedCallableUsingCurrentClassLoader、RunnableAdapter和Task类下的TaskCallable。</p> <h3 id="_2-实现callable接口的重要类分析"><a href="#_2-实现callable接口的重要类分析" class="header-anchor">#</a> 2.实现Callable接口的重要类分析</h3> <p>接下来，分析的类主要有：PrivilegedCallable、PrivilegedCallableUsingCurrentClassLoader、RunnableAdapter和Task类下的TaskCallable。虽然这些类在实际工作中很少被直接用到，但是作为一名合格的开发工程师，设置是秃顶的资深专家来说，了解并掌握这些类的实现有助你进一步理解Callable接口，并提高专业技能（头发再掉一批，哇哈哈哈。。。）。</p> <ul><li>PrivilegedCallable</li></ul> <p>PrivilegedCallable类是Callable接口的一个特殊实现类，它表明Callable对象有某种特权来访问系统的某种资源，PrivilegedCallable类的源代码如下所示。</p> <div class="language-java line-numbers-mode"><pre class="language-java"><code><span class="token comment">/**
 * A callable that runs under established access control settings
 */</span>
<span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token keyword">class</span> <span class="token class-name">PrivilegedCallable</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">T</span><span class="token punctuation">&gt;</span></span> <span class="token keyword">implements</span> <span class="token class-name">Callable</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">T</span><span class="token punctuation">&gt;</span></span> <span class="token punctuation">{</span>
	<span class="token keyword">private</span> <span class="token keyword">final</span> <span class="token class-name">Callable</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">T</span><span class="token punctuation">&gt;</span></span> task<span class="token punctuation">;</span>
	<span class="token keyword">private</span> <span class="token keyword">final</span> <span class="token class-name">AccessControlContext</span> acc<span class="token punctuation">;</span>

	<span class="token class-name">PrivilegedCallable</span><span class="token punctuation">(</span><span class="token class-name">Callable</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">T</span><span class="token punctuation">&gt;</span></span> task<span class="token punctuation">)</span> <span class="token punctuation">{</span>
		<span class="token keyword">this</span><span class="token punctuation">.</span>task <span class="token operator">=</span> task<span class="token punctuation">;</span>
		<span class="token keyword">this</span><span class="token punctuation">.</span>acc <span class="token operator">=</span> <span class="token class-name">AccessController</span><span class="token punctuation">.</span><span class="token function">getContext</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token punctuation">}</span>

	<span class="token keyword">public</span> <span class="token class-name">T</span> <span class="token function">call</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token keyword">throws</span> <span class="token class-name">Exception</span> <span class="token punctuation">{</span>
		<span class="token keyword">try</span> <span class="token punctuation">{</span>
			<span class="token keyword">return</span> <span class="token class-name">AccessController</span><span class="token punctuation">.</span><span class="token function">doPrivileged</span><span class="token punctuation">(</span>
				<span class="token keyword">new</span> <span class="token class-name">PrivilegedExceptionAction</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">T</span><span class="token punctuation">&gt;</span></span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
					<span class="token keyword">public</span> <span class="token class-name">T</span> <span class="token function">run</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token keyword">throws</span> <span class="token class-name">Exception</span> <span class="token punctuation">{</span>
						<span class="token keyword">return</span> task<span class="token punctuation">.</span><span class="token function">call</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
					<span class="token punctuation">}</span>
				<span class="token punctuation">}</span><span class="token punctuation">,</span> acc<span class="token punctuation">)</span><span class="token punctuation">;</span>
		<span class="token punctuation">}</span> <span class="token keyword">catch</span> <span class="token punctuation">(</span><span class="token class-name">PrivilegedActionException</span> e<span class="token punctuation">)</span> <span class="token punctuation">{</span>
			<span class="token keyword">throw</span> e<span class="token punctuation">.</span><span class="token function">getException</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
		<span class="token punctuation">}</span>
	<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br><span class="line-number">21</span><br><span class="line-number">22</span><br><span class="line-number">23</span><br><span class="line-number">24</span><br><span class="line-number">25</span><br></div></div><p>从PrivilegedCallable类的源代码来看，可以将PrivilegedCallable看成是对Callable接口的封装，并且这个类也继承了Callable接口。</p> <p>在PrivilegedCallable类中有两个成员变量，分别是Callable接口的实例对象和AccessControlContext类的实例对象，如下所示。</p> <div class="language-java line-numbers-mode"><pre class="language-java"><code><span class="token keyword">private</span> <span class="token keyword">final</span> <span class="token class-name">Callable</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">T</span><span class="token punctuation">&gt;</span></span> task<span class="token punctuation">;</span>
<span class="token keyword">private</span> <span class="token keyword">final</span> <span class="token class-name">AccessControlContext</span> acc<span class="token punctuation">;</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><p>其中，AccessControlContext类可以理解为一个具有系统资源访问决策的上下文类，通过这个类可以访问系统的特定资源。通过类的构造方法可以看出，在实例化AccessControlContext类的对象时，只需要传递Callable接口子类的对象即可，如下所示。</p> <div class="language-java line-numbers-mode"><pre class="language-java"><code><span class="token class-name">PrivilegedCallable</span><span class="token punctuation">(</span><span class="token class-name">Callable</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">T</span><span class="token punctuation">&gt;</span></span> task<span class="token punctuation">)</span> <span class="token punctuation">{</span>
	<span class="token keyword">this</span><span class="token punctuation">.</span>task <span class="token operator">=</span> task<span class="token punctuation">;</span>
	<span class="token keyword">this</span><span class="token punctuation">.</span>acc <span class="token operator">=</span> <span class="token class-name">AccessController</span><span class="token punctuation">.</span><span class="token function">getContext</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br></div></div><p>AccessControlContext类的对象是通过AccessController类的getContext()方法获取的，这里，查看AccessController类的getContext()方法，如下所示。</p> <div class="language-java line-numbers-mode"><pre class="language-java"><code><span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token class-name">AccessControlContext</span> <span class="token function">getContext</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
	<span class="token class-name">AccessControlContext</span> acc <span class="token operator">=</span> <span class="token function">getStackAccessControlContext</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token keyword">if</span> <span class="token punctuation">(</span>acc <span class="token operator">==</span> <span class="token keyword">null</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
		<span class="token keyword">return</span> <span class="token keyword">new</span> <span class="token class-name">AccessControlContext</span><span class="token punctuation">(</span><span class="token keyword">null</span><span class="token punctuation">,</span> <span class="token boolean">true</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token punctuation">{</span>
		<span class="token keyword">return</span> acc<span class="token punctuation">.</span><span class="token function">optimize</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br></div></div><p>通过AccessController的getContext()方法可以看出，首先通过getStackAccessControlContext()方法来获取AccessControlContext对象实例。如果获取的AccessControlContext对象实例为空，则通过调用AccessControlContext类的构造方法实例化，否则，调用AccessControlContext对象实例的optimize()方法返回AccessControlContext对象实例。</p> <p>这里，我们先看下getStackAccessControlContext()方法是个什么鬼。</p> <div class="language-java line-numbers-mode"><pre class="language-java"><code><span class="token keyword">private</span> <span class="token keyword">static</span> <span class="token keyword">native</span> <span class="token class-name">AccessControlContext</span> <span class="token function">getStackAccessControlContext</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><p>原来是个本地方法，方法的字面意思就是获取能够访问系统栈的决策上下文对象。</p> <p>接下来，我们回到PrivilegedCallable类的call()方法，如下所示。</p> <div class="language-java line-numbers-mode"><pre class="language-java"><code><span class="token keyword">public</span> <span class="token class-name">T</span> <span class="token function">call</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token keyword">throws</span> <span class="token class-name">Exception</span> <span class="token punctuation">{</span>
	<span class="token keyword">try</span> <span class="token punctuation">{</span>
		<span class="token keyword">return</span> <span class="token class-name">AccessController</span><span class="token punctuation">.</span><span class="token function">doPrivileged</span><span class="token punctuation">(</span>
			<span class="token keyword">new</span> <span class="token class-name">PrivilegedExceptionAction</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">T</span><span class="token punctuation">&gt;</span></span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
				<span class="token keyword">public</span> <span class="token class-name">T</span> <span class="token function">run</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token keyword">throws</span> <span class="token class-name">Exception</span> <span class="token punctuation">{</span>
					<span class="token keyword">return</span> task<span class="token punctuation">.</span><span class="token function">call</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
				<span class="token punctuation">}</span>
			<span class="token punctuation">}</span><span class="token punctuation">,</span> acc<span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token punctuation">}</span> <span class="token keyword">catch</span> <span class="token punctuation">(</span><span class="token class-name">PrivilegedActionException</span> e<span class="token punctuation">)</span> <span class="token punctuation">{</span>
		<span class="token keyword">throw</span> e<span class="token punctuation">.</span><span class="token function">getException</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br></div></div><p>通过调用AccessController.doPrivileged()方法，传递PrivilegedExceptionAction。接口对象和AccessControlContext对象，并最终返回泛型的实例对象。</p> <p>首先，看下AccessController.doPrivileged()方法，如下所示。</p> <div class="language-java line-numbers-mode"><pre class="language-java"><code><span class="token annotation punctuation">@CallerSensitive</span>
<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">native</span> <span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">T</span><span class="token punctuation">&gt;</span></span> <span class="token class-name">T</span>
    <span class="token function">doPrivileged</span><span class="token punctuation">(</span><span class="token class-name">PrivilegedExceptionAction</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">T</span><span class="token punctuation">&gt;</span></span> action<span class="token punctuation">,</span>
                 <span class="token class-name">AccessControlContext</span> context<span class="token punctuation">)</span>
    <span class="token keyword">throws</span> <span class="token class-name">PrivilegedActionException</span><span class="token punctuation">;</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br></div></div><p>可以看到，又是一个本地方法。也就是说，最终的执行情况是将PrivilegedExceptionAction接口对象和AccessControlContext对象实例传递给这个本地方法执行。并且在PrivilegedExceptionAction接口对象的run()方法中调用Callable接口的call()方法来执行最终的业务逻辑，并且返回泛型对象。</p> <ul><li>PrivilegedCallableUsingCurrentClassLoader</li></ul> <p>此类表示为在已经建立的特定访问控制和当前的类加载器下运行的Callable类，源代码如下所示。</p> <div class="language-java line-numbers-mode"><pre class="language-java"><code><span class="token comment">/**
 * A callable that runs under established access control settings and
 * current ClassLoader
 */</span>
<span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token keyword">class</span> <span class="token class-name">PrivilegedCallableUsingCurrentClassLoader</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">T</span><span class="token punctuation">&gt;</span></span> <span class="token keyword">implements</span> <span class="token class-name">Callable</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">T</span><span class="token punctuation">&gt;</span></span> <span class="token punctuation">{</span>
	<span class="token keyword">private</span> <span class="token keyword">final</span> <span class="token class-name">Callable</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">T</span><span class="token punctuation">&gt;</span></span> task<span class="token punctuation">;</span>
	<span class="token keyword">private</span> <span class="token keyword">final</span> <span class="token class-name">AccessControlContext</span> acc<span class="token punctuation">;</span>
	<span class="token keyword">private</span> <span class="token keyword">final</span> <span class="token class-name">ClassLoader</span> ccl<span class="token punctuation">;</span>

	<span class="token class-name">PrivilegedCallableUsingCurrentClassLoader</span><span class="token punctuation">(</span><span class="token class-name">Callable</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">T</span><span class="token punctuation">&gt;</span></span> task<span class="token punctuation">)</span> <span class="token punctuation">{</span>
		<span class="token class-name">SecurityManager</span> sm <span class="token operator">=</span> <span class="token class-name">System</span><span class="token punctuation">.</span><span class="token function">getSecurityManager</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
		<span class="token keyword">if</span> <span class="token punctuation">(</span>sm <span class="token operator">!=</span> <span class="token keyword">null</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
			sm<span class="token punctuation">.</span><span class="token function">checkPermission</span><span class="token punctuation">(</span><span class="token class-name">SecurityConstants</span><span class="token punctuation">.</span>GET_CLASSLOADER_PERMISSION<span class="token punctuation">)</span><span class="token punctuation">;</span>
			sm<span class="token punctuation">.</span><span class="token function">checkPermission</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">RuntimePermission</span><span class="token punctuation">(</span><span class="token string">&quot;setContextClassLoader&quot;</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
		<span class="token punctuation">}</span>
		<span class="token keyword">this</span><span class="token punctuation">.</span>task <span class="token operator">=</span> task<span class="token punctuation">;</span>
		<span class="token keyword">this</span><span class="token punctuation">.</span>acc <span class="token operator">=</span> <span class="token class-name">AccessController</span><span class="token punctuation">.</span><span class="token function">getContext</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
		<span class="token keyword">this</span><span class="token punctuation">.</span>ccl <span class="token operator">=</span> <span class="token class-name">Thread</span><span class="token punctuation">.</span><span class="token function">currentThread</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">getContextClassLoader</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token punctuation">}</span>

	<span class="token keyword">public</span> <span class="token class-name">T</span> <span class="token function">call</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token keyword">throws</span> <span class="token class-name">Exception</span> <span class="token punctuation">{</span>
		<span class="token keyword">try</span> <span class="token punctuation">{</span>
			<span class="token keyword">return</span> <span class="token class-name">AccessController</span><span class="token punctuation">.</span><span class="token function">doPrivileged</span><span class="token punctuation">(</span>
				<span class="token keyword">new</span> <span class="token class-name">PrivilegedExceptionAction</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">T</span><span class="token punctuation">&gt;</span></span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
					<span class="token keyword">public</span> <span class="token class-name">T</span> <span class="token function">run</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token keyword">throws</span> <span class="token class-name">Exception</span> <span class="token punctuation">{</span>
						<span class="token class-name">Thread</span> t <span class="token operator">=</span> <span class="token class-name">Thread</span><span class="token punctuation">.</span><span class="token function">currentThread</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
						<span class="token class-name">ClassLoader</span> cl <span class="token operator">=</span> t<span class="token punctuation">.</span><span class="token function">getContextClassLoader</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
						<span class="token keyword">if</span> <span class="token punctuation">(</span>ccl <span class="token operator">==</span> cl<span class="token punctuation">)</span> <span class="token punctuation">{</span>
							<span class="token keyword">return</span> task<span class="token punctuation">.</span><span class="token function">call</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
						<span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token punctuation">{</span>
							t<span class="token punctuation">.</span><span class="token function">setContextClassLoader</span><span class="token punctuation">(</span>ccl<span class="token punctuation">)</span><span class="token punctuation">;</span>
							<span class="token keyword">try</span> <span class="token punctuation">{</span>
								<span class="token keyword">return</span> task<span class="token punctuation">.</span><span class="token function">call</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
							<span class="token punctuation">}</span> <span class="token keyword">finally</span> <span class="token punctuation">{</span>
								t<span class="token punctuation">.</span><span class="token function">setContextClassLoader</span><span class="token punctuation">(</span>cl<span class="token punctuation">)</span><span class="token punctuation">;</span>
							<span class="token punctuation">}</span>
						<span class="token punctuation">}</span>
					<span class="token punctuation">}</span>
				<span class="token punctuation">}</span><span class="token punctuation">,</span> acc<span class="token punctuation">)</span><span class="token punctuation">;</span>
		<span class="token punctuation">}</span> <span class="token keyword">catch</span> <span class="token punctuation">(</span><span class="token class-name">PrivilegedActionException</span> e<span class="token punctuation">)</span> <span class="token punctuation">{</span>
			<span class="token keyword">throw</span> e<span class="token punctuation">.</span><span class="token function">getException</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
		<span class="token punctuation">}</span>
	<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br><span class="line-number">21</span><br><span class="line-number">22</span><br><span class="line-number">23</span><br><span class="line-number">24</span><br><span class="line-number">25</span><br><span class="line-number">26</span><br><span class="line-number">27</span><br><span class="line-number">28</span><br><span class="line-number">29</span><br><span class="line-number">30</span><br><span class="line-number">31</span><br><span class="line-number">32</span><br><span class="line-number">33</span><br><span class="line-number">34</span><br><span class="line-number">35</span><br><span class="line-number">36</span><br><span class="line-number">37</span><br><span class="line-number">38</span><br><span class="line-number">39</span><br><span class="line-number">40</span><br><span class="line-number">41</span><br><span class="line-number">42</span><br><span class="line-number">43</span><br><span class="line-number">44</span><br></div></div><p>这个类理解起来比较简单，首先，在类中定义了三个成员变量，如下所示。</p> <div class="language-java line-numbers-mode"><pre class="language-java"><code><span class="token keyword">private</span> <span class="token keyword">final</span> <span class="token class-name">Callable</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">T</span><span class="token punctuation">&gt;</span></span> task<span class="token punctuation">;</span>
<span class="token keyword">private</span> <span class="token keyword">final</span> <span class="token class-name">AccessControlContext</span> acc<span class="token punctuation">;</span>
<span class="token keyword">private</span> <span class="token keyword">final</span> <span class="token class-name">ClassLoader</span> ccl<span class="token punctuation">;</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><p>接下来，通过构造方法注入Callable对象，在构造方法中，首先获取系统安全管理器对象实例，通过系统安全管理器对象实例检查是否具有获取ClassLoader和设置ContextClassLoader的权限。并在构造方法中为三个成员变量赋值，如下所示。</p> <div class="language-java line-numbers-mode"><pre class="language-java"><code><span class="token class-name">PrivilegedCallableUsingCurrentClassLoader</span><span class="token punctuation">(</span><span class="token class-name">Callable</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">T</span><span class="token punctuation">&gt;</span></span> task<span class="token punctuation">)</span> <span class="token punctuation">{</span>
	<span class="token class-name">SecurityManager</span> sm <span class="token operator">=</span> <span class="token class-name">System</span><span class="token punctuation">.</span><span class="token function">getSecurityManager</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token keyword">if</span> <span class="token punctuation">(</span>sm <span class="token operator">!=</span> <span class="token keyword">null</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
		sm<span class="token punctuation">.</span><span class="token function">checkPermission</span><span class="token punctuation">(</span><span class="token class-name">SecurityConstants</span><span class="token punctuation">.</span>GET_CLASSLOADER_PERMISSION<span class="token punctuation">)</span><span class="token punctuation">;</span>
		sm<span class="token punctuation">.</span><span class="token function">checkPermission</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">RuntimePermission</span><span class="token punctuation">(</span><span class="token string">&quot;setContextClassLoader&quot;</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token punctuation">}</span>
	<span class="token keyword">this</span><span class="token punctuation">.</span>task <span class="token operator">=</span> task<span class="token punctuation">;</span>
	<span class="token keyword">this</span><span class="token punctuation">.</span>acc <span class="token operator">=</span> <span class="token class-name">AccessController</span><span class="token punctuation">.</span><span class="token function">getContext</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token keyword">this</span><span class="token punctuation">.</span>ccl <span class="token operator">=</span> <span class="token class-name">Thread</span><span class="token punctuation">.</span><span class="token function">currentThread</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">getContextClassLoader</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br></div></div><p>接下来，通过调用call()方法来执行具体的业务逻辑，如下所示。</p> <div class="language-java line-numbers-mode"><pre class="language-java"><code><span class="token keyword">public</span> <span class="token class-name">T</span> <span class="token function">call</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token keyword">throws</span> <span class="token class-name">Exception</span> <span class="token punctuation">{</span>
	<span class="token keyword">try</span> <span class="token punctuation">{</span>
		<span class="token keyword">return</span> <span class="token class-name">AccessController</span><span class="token punctuation">.</span><span class="token function">doPrivileged</span><span class="token punctuation">(</span>
			<span class="token keyword">new</span> <span class="token class-name">PrivilegedExceptionAction</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">T</span><span class="token punctuation">&gt;</span></span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
				<span class="token keyword">public</span> <span class="token class-name">T</span> <span class="token function">run</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token keyword">throws</span> <span class="token class-name">Exception</span> <span class="token punctuation">{</span>
					<span class="token class-name">Thread</span> t <span class="token operator">=</span> <span class="token class-name">Thread</span><span class="token punctuation">.</span><span class="token function">currentThread</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
					<span class="token class-name">ClassLoader</span> cl <span class="token operator">=</span> t<span class="token punctuation">.</span><span class="token function">getContextClassLoader</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
					<span class="token keyword">if</span> <span class="token punctuation">(</span>ccl <span class="token operator">==</span> cl<span class="token punctuation">)</span> <span class="token punctuation">{</span>
						<span class="token keyword">return</span> task<span class="token punctuation">.</span><span class="token function">call</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
					<span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token punctuation">{</span>
						t<span class="token punctuation">.</span><span class="token function">setContextClassLoader</span><span class="token punctuation">(</span>ccl<span class="token punctuation">)</span><span class="token punctuation">;</span>
						<span class="token keyword">try</span> <span class="token punctuation">{</span>
							<span class="token keyword">return</span> task<span class="token punctuation">.</span><span class="token function">call</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
						<span class="token punctuation">}</span> <span class="token keyword">finally</span> <span class="token punctuation">{</span>
							t<span class="token punctuation">.</span><span class="token function">setContextClassLoader</span><span class="token punctuation">(</span>cl<span class="token punctuation">)</span><span class="token punctuation">;</span>
						<span class="token punctuation">}</span>
					<span class="token punctuation">}</span>
				<span class="token punctuation">}</span>
			<span class="token punctuation">}</span><span class="token punctuation">,</span> acc<span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token punctuation">}</span> <span class="token keyword">catch</span> <span class="token punctuation">(</span><span class="token class-name">PrivilegedActionException</span> e<span class="token punctuation">)</span> <span class="token punctuation">{</span>
		<span class="token keyword">throw</span> e<span class="token punctuation">.</span><span class="token function">getException</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br><span class="line-number">21</span><br><span class="line-number">22</span><br><span class="line-number">23</span><br></div></div><p>在call()方法中同样是通过调用AccessController类的本地方法doPrivileged，传递PrivilegedExceptionAction接口的实例对象和AccessControlContext类的对象实例。</p> <p>具体执行逻辑为：在PrivilegedExceptionAction对象的run()方法中获取当前线程的ContextClassLoader对象，如果在构造方法中获取的ClassLoader对象与此处的ContextClassLoader对象是同一个对象（不止对象实例相同，而且内存地址也相同），则直接调用Callable对象的call()方法返回结果。否则，将PrivilegedExceptionAction对象的run()方法中的当前线程的ContextClassLoader设置为在构造方法中获取的类加载器对象，接下来，再调用Callable对象的call()方法返回结果。最终将当前线程的ContextClassLoader重置为之前的ContextClassLoader。</p> <ul><li>RunnableAdapter</li></ul> <p>RunnableAdapter类比较简单，给定运行的任务和结果，运行给定的任务并返回给定的结果，源代码如下所示。</p> <div class="language-java line-numbers-mode"><pre class="language-java"><code><span class="token comment">/**
 * A callable that runs given task and returns given result
 */</span>
<span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token keyword">class</span> <span class="token class-name">RunnableAdapter</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">T</span><span class="token punctuation">&gt;</span></span> <span class="token keyword">implements</span> <span class="token class-name">Callable</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">T</span><span class="token punctuation">&gt;</span></span> <span class="token punctuation">{</span>
	<span class="token keyword">final</span> <span class="token class-name">Runnable</span> task<span class="token punctuation">;</span>
	<span class="token keyword">final</span> <span class="token class-name">T</span> result<span class="token punctuation">;</span>
	<span class="token class-name">RunnableAdapter</span><span class="token punctuation">(</span><span class="token class-name">Runnable</span> task<span class="token punctuation">,</span> <span class="token class-name">T</span> result<span class="token punctuation">)</span> <span class="token punctuation">{</span>
		<span class="token keyword">this</span><span class="token punctuation">.</span>task <span class="token operator">=</span> task<span class="token punctuation">;</span>
		<span class="token keyword">this</span><span class="token punctuation">.</span>result <span class="token operator">=</span> result<span class="token punctuation">;</span>
	<span class="token punctuation">}</span>
	<span class="token keyword">public</span> <span class="token class-name">T</span> <span class="token function">call</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
		task<span class="token punctuation">.</span><span class="token function">run</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
		<span class="token keyword">return</span> result<span class="token punctuation">;</span>
	<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br></div></div><ul><li>TaskCallable</li></ul> <p>TaskCallable类是javafx.concurrent.Task类的静态内部类，TaskCallable类主要是实现了Callable接口并且被定义为FutureTask的类，并且在这个类中允许我们拦截call()方法来更新task任务的状态。源代码如下所示。</p> <div class="language-java line-numbers-mode"><pre class="language-java"><code><span class="token keyword">private</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token keyword">class</span> <span class="token class-name">TaskCallable</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">V</span><span class="token punctuation">&gt;</span></span> <span class="token keyword">implements</span> <span class="token class-name">Callable</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">V</span><span class="token punctuation">&gt;</span></span> <span class="token punctuation">{</span>

	<span class="token keyword">private</span> <span class="token class-name">Task</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">V</span><span class="token punctuation">&gt;</span></span> task<span class="token punctuation">;</span>
	<span class="token keyword">private</span> <span class="token class-name">TaskCallable</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token punctuation">}</span>

	<span class="token annotation punctuation">@Override</span> 
	<span class="token keyword">public</span> <span class="token class-name">V</span> <span class="token function">call</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token keyword">throws</span> <span class="token class-name">Exception</span> <span class="token punctuation">{</span>
		task<span class="token punctuation">.</span>started <span class="token operator">=</span> <span class="token boolean">true</span><span class="token punctuation">;</span>
		task<span class="token punctuation">.</span><span class="token function">runLater</span><span class="token punctuation">(</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">-&gt;</span> <span class="token punctuation">{</span>
			task<span class="token punctuation">.</span><span class="token function">setState</span><span class="token punctuation">(</span><span class="token class-name">State</span><span class="token punctuation">.</span>SCHEDULED<span class="token punctuation">)</span><span class="token punctuation">;</span>
			task<span class="token punctuation">.</span><span class="token function">setState</span><span class="token punctuation">(</span><span class="token class-name">State</span><span class="token punctuation">.</span>RUNNING<span class="token punctuation">)</span><span class="token punctuation">;</span>
		<span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
		<span class="token keyword">try</span> <span class="token punctuation">{</span>
			<span class="token keyword">final</span> <span class="token class-name">V</span> result <span class="token operator">=</span> task<span class="token punctuation">.</span><span class="token function">call</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
			<span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token operator">!</span>task<span class="token punctuation">.</span><span class="token function">isCancelled</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
				task<span class="token punctuation">.</span><span class="token function">runLater</span><span class="token punctuation">(</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">-&gt;</span> <span class="token punctuation">{</span>
					task<span class="token punctuation">.</span><span class="token function">updateValue</span><span class="token punctuation">(</span>result<span class="token punctuation">)</span><span class="token punctuation">;</span>
					task<span class="token punctuation">.</span><span class="token function">setState</span><span class="token punctuation">(</span><span class="token class-name">State</span><span class="token punctuation">.</span>SUCCEEDED<span class="token punctuation">)</span><span class="token punctuation">;</span>
				<span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
				<span class="token keyword">return</span> result<span class="token punctuation">;</span>
			<span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token punctuation">{</span>
				<span class="token keyword">return</span> <span class="token keyword">null</span><span class="token punctuation">;</span>
			<span class="token punctuation">}</span>
		<span class="token punctuation">}</span> <span class="token keyword">catch</span> <span class="token punctuation">(</span><span class="token keyword">final</span> <span class="token class-name">Throwable</span> th<span class="token punctuation">)</span> <span class="token punctuation">{</span>
			task<span class="token punctuation">.</span><span class="token function">runLater</span><span class="token punctuation">(</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">-&gt;</span> <span class="token punctuation">{</span>
				task<span class="token punctuation">.</span><span class="token function">_setException</span><span class="token punctuation">(</span>th<span class="token punctuation">)</span><span class="token punctuation">;</span>
				task<span class="token punctuation">.</span><span class="token function">setState</span><span class="token punctuation">(</span><span class="token class-name">State</span><span class="token punctuation">.</span>FAILED<span class="token punctuation">)</span><span class="token punctuation">;</span>
			<span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
			<span class="token keyword">if</span> <span class="token punctuation">(</span>th <span class="token keyword">instanceof</span> <span class="token class-name">Exception</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
				<span class="token keyword">throw</span> <span class="token punctuation">(</span><span class="token class-name">Exception</span><span class="token punctuation">)</span> th<span class="token punctuation">;</span>
			<span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token punctuation">{</span>
				<span class="token keyword">throw</span> <span class="token keyword">new</span> <span class="token class-name">Exception</span><span class="token punctuation">(</span>th<span class="token punctuation">)</span><span class="token punctuation">;</span>
			<span class="token punctuation">}</span>
		<span class="token punctuation">}</span>
	<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br><span class="line-number">21</span><br><span class="line-number">22</span><br><span class="line-number">23</span><br><span class="line-number">24</span><br><span class="line-number">25</span><br><span class="line-number">26</span><br><span class="line-number">27</span><br><span class="line-number">28</span><br><span class="line-number">29</span><br><span class="line-number">30</span><br><span class="line-number">31</span><br><span class="line-number">32</span><br><span class="line-number">33</span><br><span class="line-number">34</span><br><span class="line-number">35</span><br><span class="line-number">36</span><br></div></div><p>从TaskCallable类的源代码可以看出，只定义了一个Task类型的成员变量。下面主要分析TaskCallable类的call()方法。</p> <p>当程序的执行进入到call()方法时，首先将task对象的started属性设置为true，表示任务已经开始，并且将任务的状态依次设置为State.SCHEDULED和State.RUNNING，依次触发任务的调度事件和运行事件。如下所示。</p> <div class="language-java line-numbers-mode"><pre class="language-java"><code>task<span class="token punctuation">.</span>started <span class="token operator">=</span> <span class="token boolean">true</span><span class="token punctuation">;</span>
task<span class="token punctuation">.</span><span class="token function">runLater</span><span class="token punctuation">(</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">-&gt;</span> <span class="token punctuation">{</span>
	task<span class="token punctuation">.</span><span class="token function">setState</span><span class="token punctuation">(</span><span class="token class-name">State</span><span class="token punctuation">.</span>SCHEDULED<span class="token punctuation">)</span><span class="token punctuation">;</span>
	task<span class="token punctuation">.</span><span class="token function">setState</span><span class="token punctuation">(</span><span class="token class-name">State</span><span class="token punctuation">.</span>RUNNING<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br></div></div><p>接下来，在try代码块中执行Task对象的call()方法，返回泛型对象。如果任务没有被取消，则更新任务的缓存，将调用call()方法返回的泛型对象绑定到Task对象中的ObjectProperty<V>对象中，其中，ObjectProperty<V>在Task类中的定义如下。</V></V></p> <div class="language-java line-numbers-mode"><pre class="language-java"><code><span class="token keyword">private</span> <span class="token keyword">final</span> <span class="token class-name">ObjectProperty</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">V</span><span class="token punctuation">&gt;</span></span> value <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">SimpleObjectProperty</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token punctuation">&gt;</span></span><span class="token punctuation">(</span><span class="token keyword">this</span><span class="token punctuation">,</span> <span class="token string">&quot;value&quot;</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><p>接下来，将任务的状态设置为成功状态。如下所示。</p> <div class="language-java line-numbers-mode"><pre class="language-java"><code><span class="token keyword">try</span> <span class="token punctuation">{</span>
	<span class="token keyword">final</span> <span class="token class-name">V</span> result <span class="token operator">=</span> task<span class="token punctuation">.</span><span class="token function">call</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token operator">!</span>task<span class="token punctuation">.</span><span class="token function">isCancelled</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
		task<span class="token punctuation">.</span><span class="token function">runLater</span><span class="token punctuation">(</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">-&gt;</span> <span class="token punctuation">{</span>
			task<span class="token punctuation">.</span><span class="token function">updateValue</span><span class="token punctuation">(</span>result<span class="token punctuation">)</span><span class="token punctuation">;</span>
			task<span class="token punctuation">.</span><span class="token function">setState</span><span class="token punctuation">(</span><span class="token class-name">State</span><span class="token punctuation">.</span>SUCCEEDED<span class="token punctuation">)</span><span class="token punctuation">;</span>
		<span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
		<span class="token keyword">return</span> result<span class="token punctuation">;</span>
	<span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token punctuation">{</span>
		<span class="token keyword">return</span> <span class="token keyword">null</span><span class="token punctuation">;</span>
	<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br></div></div><p>如果程序抛出了异常或者错误，会进入catch()代码块，设置Task对象的Exception信息并将状态设置为State.FAILED，也就是将任务标记为失败。接下来，判断异常或错误的类型，如果是Exception类型的异常，则直接强转为Exception类型的异常并抛出。否则，将异常或者错误封装为Exception对象并抛出，如下所示。</p> <div class="language-java line-numbers-mode"><pre class="language-java"><code><span class="token keyword">catch</span> <span class="token punctuation">(</span><span class="token keyword">final</span> <span class="token class-name">Throwable</span> th<span class="token punctuation">)</span> <span class="token punctuation">{</span>
	task<span class="token punctuation">.</span><span class="token function">runLater</span><span class="token punctuation">(</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">-&gt;</span> <span class="token punctuation">{</span>
		task<span class="token punctuation">.</span><span class="token function">_setException</span><span class="token punctuation">(</span>th<span class="token punctuation">)</span><span class="token punctuation">;</span>
		task<span class="token punctuation">.</span><span class="token function">setState</span><span class="token punctuation">(</span><span class="token class-name">State</span><span class="token punctuation">.</span>FAILED<span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token keyword">if</span> <span class="token punctuation">(</span>th <span class="token keyword">instanceof</span> <span class="token class-name">Exception</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
		<span class="token keyword">throw</span> <span class="token punctuation">(</span><span class="token class-name">Exception</span><span class="token punctuation">)</span> th<span class="token punctuation">;</span>
	<span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token punctuation">{</span>
		<span class="token keyword">throw</span> <span class="token keyword">new</span> <span class="token class-name">Exception</span><span class="token punctuation">(</span>th<span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br></div></div><p><strong>记住：你比别人强的地方，不是你做过多少年的CRUD工作，而是你比别人掌握了更多深入的技能。不要总停留在CRUD的表面工作，理解并掌握底层原理并熟悉源码实现，并形成自己的抽象思维能力，做到灵活运用，才是你突破瓶颈，脱颖而出的重要方向！</strong></p> <p><strong>最后，作为一名合格（发际线比较高）的开发人员或者资深（秃顶）的工程师和架构师来说，理解原理和掌握源码，并形成自己的抽象思维能力，灵活运用是你必须掌握的技能。</strong></p> <p><strong>好了，今天就到这儿吧，我是冰河，我们下期见~~</strong></p> <h2 id="写在最后"><a href="#写在最后" class="header-anchor">#</a> 写在最后</h2> <blockquote><p>如果觉得文章对你有点帮助，请微信搜索并关注「 <strong>冰河技术</strong> 」微信公众号，跟冰河学习高并发编程技术。</p></blockquote> <p>最后，附上并发编程需要掌握的核心技能知识图，祝大家在学习并发编程时，少走弯路。</p> <p><img alt="" data-src="https://img-blog.csdnimg.cn/20200322144644983.jpg?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2wxMDI4Mzg2ODA0,size_16,color_FFFFFF,t_70#pic_center" loading="lazy" class="lazy"></p> <blockquote><p>如果你觉得冰河写的还不错，请微信搜索并关注「 <strong>冰河技术</strong> 」微信公众号，跟冰河学习高并发、分布式、微服务、大数据、互联网和云原生技术，「 <strong>冰河技术</strong> 」微信公众号更新了大量技术专题，每一篇技术文章干货满满！不少读者已经通过阅读「 <strong>冰河技术</strong> 」微信公众号文章，吊打面试官，成功跳槽到大厂；也有不少读者实现了技术上的飞跃，成为公司的技术骨干！如果你也想像他们一样提升自己的能力，实现技术能力的飞跃，进大厂，升职加薪，那就关注「 <strong>冰河技术</strong> 」微信公众号吧，每天更新超硬核技术干货，让你对如何提升技术能力不再迷茫！</p></blockquote> <p><img alt="" data-src="https://img-blog.csdnimg.cn/20200906013715889.png" loading="lazy" class="lazy"></p></div> <footer class="page-edit"><div class="edit-link"><a href="https://github.com/binghe001/BingheGuide/edit/master/docs/md/concurrent/source/2020-03-30-003-深入解析Callable接口.md" target="_blank" rel="noopener noreferrer">在 GitHub 上编辑此页</a> <span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></div> <div class="last-updated"><span class="prefix">上次更新: </span> <span class="time">2022/5/23</span></div></footer> <div class="page-nav"><p class="inner"><span class="prev">
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